Modern electrical power distribution systems supply power to a large number of electrical loads, such as residences, factories or businesses. The power consumed by each electrical load is separately measured by an electrical metering device, such as an induction or electronic type watthour meter. Many electrical power distribution systems include tens of thousands, hundreds of thousands or more metering devices.
Induction type watthour meters have historically been utilized to measure electrical power consumption. Recently, however, an increasing number of electrical metering devices, such as electronic type watthour meters, have been employed to measure electrical energy consumption. The use of electronic type watthour meters has increased, in part, since electronic meters can measure several quantities in addition to tabulating the kilowatt hours of power consumed by the corresponding load. For example, electronic type watthour meters can measure the power factor, kilovolt amperes ("KVA"), and reactive volt amperes of the power consumed by the load.
The increased metering flexibility and capacity provided by electronic type watthour meters is due, at least in part, to the electronic acquisition, integration and processing of the measured electrical consumption of the load by, for example, an electronic processor or controller. In addition, electronic type watthour meters may be reprogrammed to alter their operation once they have been installed so as to offer additional metering flexibility.
In order to "read" the electrical metering device to determine the power consumption of the associated load or to reprogram the electrical metering device, electrical metering devices include means for externally communicating. According to one method of communicating with electronic type watthour meters, a display associated with the meter is observed. Alternatively, the signals may be optically transmitted to and received from an electronic type watthour meter having an optical port with a corresponding optical probe. Both communications methods, however, require the meter to be physically visited in the field.
Since modern electrical power distribution systems include tens of thousands, hundreds of thousands or more metering devices, various communications methods, including power line communications systems, have been employed to transfer signals to and receive signals from electronic type watthour meters without having to physically visit the meters in the field. Many different types of signals may be transmitted such as signals which are indicative of the quantities measured by the metering device, such as kilowatt hours of power consumed, so as to permit the meter to be "read" from a remote location. The signals may also include revised instructions to reprogram the electronic meter.
One such communications system-is the UCNet.TM. system marketed by General Electric Company, assignee of the present invention. The UCNet.TM. system is described and illustrated in a publication entitled "GE UCNet System" by GE Meter and Control of Somersworth, N.H., which bears document number GEA12091 9/91 7M. The UCNet.TM. system is also described in a publication entitled "Engineering Presentation to AEIC/EEI Meter and Service Committees" by GE Meter and Control which bears document number GET-6638.22 9/91 (3M). The disclosures of both publications are incorporated herein by reference.
A typical power line communications system, such as that illustrated in U.S. Pat. No. 4,749,992 to Fitzemeyer which is incorporated herein by reference, includes a central control station, typically referred to as a system-control center, which transmits signals to one or more radio towers. The signals may be transmitted to the radio tower by radio frequency ("RF") transmission or by cable television or telephone lines or by a satellite or microwave link. Each radio tower, in turn, rebroadcasts the signals to a plurality of fixed nodes, such as by RF transmission.
Each fixed node in a typical power line. communications system is generally a remote local relay module associated with a specific distribution transformer. Each relay module then transmits the signals to the individual, electrical metering devices via the power lines which connect the associated distribution transformer to the metering devices. Thus, the power lines, in addition to transferring electrical power to the metering device and the electrical load, also acts as a communications bus for communications between the node and the metering devices. Accordingly, a local area network is established between a fixed node and the electrical metering devices operably connected to the secondary side of the distribution transformer associated with the fixed node.
The electronic type watthour meters coupled to the electrical loads of the distribution transformer include a modem for receiving and translating the signals transmitted via the power lines. The modem thereafter provides the translated signal to the controller or processor of the electronic type watthour meter. The modem is bidirectional so as to also transmit signals from the electronic type watthour meter on the power lines.
The fixed node and each electronic type watthour meter within a local area network is assigned an predetermined address. As explained in more detail in an interim standard published by the Electronic Industries Association of Washington, D.C. in October 1992 which is entitled "EIA Home Automation System (CEBus)", the standard CEBus protocol includes seven hierarchical layers. The data link layer includes fields for the actual command or signal to be transmitted, designated the information field, as well as fields for the source address and the destination address of the signal. Accordingly, the device which sent and the device which is to receive the signal are identified by their respective predefined addresses.
As discussed, each fixed node of a power line communications system is typically associated with a distribution transformer. Therefore, each fixed node may communicate via the power line with the electrical loads, i.e. the homes or businesses, connected to the distribution transformer. Although the number of loads connected to a distribution transformer may vary, five to ten electrical loads are typically connected via the power lines to the distribution transformer and, in turn, to the associated fixed node.
Since a modern electrical power distribution system includes tens of thousands, hundreds of thousands or more electronic type watthour meters, a power line communications system generally includes hundreds, thousands or more fixed nodes. Each fixed node is relatively expensive since it must be adapted to communicate not only with each electrical metering device operably connected to the fixed node, but also with the system control center. Each fixed node must also include relatively sophisticated data processing capabilities so as to reliably convert the signals received via the power line to appropriate radio frequency signals for transmission to the system control center. Thus, the number and cost of the fixed nodes employed by a power line communications system is large.
U.S. Pat. No. 4,614,945 (the "'945 patent") which issued on Sep. 30, 1986 to Brunius, et al. and U.S. Pat. No. 4,799,059 (the "'059 patent") which issued on Jan. 17, 1989 to Grindahl, et al. illustrate one method to replace fixed nodes within a communications system of an electrical power distribution system with a mobile instrument monitoring system. The mobile instrument monitoring system of the '945 and '059 patents includes a transmitter activator for prompting RF transponder units which are operably connected to remotely located instruments at a remote location. In response to the prompting, the RF transponders transmit messages over a predetermined RF transmission band to the mobile instrument monitoring system.
The mobile instrument monitoring system of the '945 and the '059 patents also includes a plurality of RF receivers which are tuned to collectively receive the transponder transmissions. Upon receipt, the instrument monitoring system identifies the transmitting transponders and processes their respective messages. The account data resulting from the signal processing is stored within the mobile instrument monitoring system. At the end of the day or after all meters have been read, the stored account data may be transferred to a utility billing system, such as through transfer of a storage medium, i.e. a computer diskette, or through a serial data interface.
It would be desirable to decrease the number of fixed nodes in the communications system of an electrical power distributing system and thus decrease the cost of the system, while still communicating with each electrical metering device. In addition, in contrast to the mobile instrument monitoring system of the '945 and '059 patents which receives, processes and stores the account information until the end of the day or until all meters have been read, it would be desirable to promptly provide the system control center with the information obtained from the electrical metering devices. Thus, the system control center could further process the information obtained from the electrical metering devices prior to the end of the day or before all of the meters have been read.